Corrosion-resistant chromium-manganese-iron alloys



Patented Dec. 26, 1939 UNITED STATES CORRO SION-RESISTAN T CHROMIUM-MAN-GANESE-IRON ALLOYS Alfred Kropf, Wetzlar, Lahn, Germany No Drawing.Application October 1,1936, Se-

rial No. 103,527. In Germany April 8, 1935 1 Claim.

The present invention relates to ferrous-chromium-manganese alloys whichapproach German silver in appearance and properties and may be used as asubstitute therefor.

Manganese has heretofore been suggested as a substitute for the nickelof chromium-nickel steels for increasing the corrosion resistance ofsuch steels. In these known alloys, however, the chromium contentexceeds the manganese content. These alloys as a result, unlike silverand German silver, possess a high ultimate strength and little abilityto be stamped. Besides they do not have a silvery sheen and this factalone absolutely precludes their use as substitutes for silver andGerman silver. Finally they are difficult to plate with silver and, whenplated, do not take a plating that is durable. They cannot, therefore,hope to compete with silver or German silver in those fields in whichthese metals find such extensive use.

An object of this invention is to produce an alloy of manganese andchromium which has an appearance like that of silver and which can beused as a substitute for silver and German silver.

An additional object is to produce a'corrosion resistantmanganese-chromium alloy that can be readily worked and shapedmechanically either in the warm or cold condition.

I have now discovered that alloys similar in practically every respectto German silver can be obtained by including in an iron-chromium-copperalloy a quantity of manganese in excess of the chromium content, whilemaintaining the chromium content below 25%. Generally speaking, thechromium content will range from 3 to 25% and the manganese content from'I to 50%. The copper content is usually relatively low, at no timeexceeding 10%. As a matter of fact, the presence of copper is notabsolutely essential. However, copper has a favorable influence on thecorrosion resistance and extensibility of the alloys and, therefore, thepresence of small amounts of copper is recommended. Further copper hasthe ability of imparting a warm color tone verging on yellow to thealloys. Where such an appearance is desirable, copper should be presentin amounts of up to about 5%, the quantity of manganese at the same timenot exceeding about 35%. It may be said as a general rule with regard tocopper that the quantity thereof should increase as the quantity ofmanganese increases and the quantity of chromium decreases. Carbonshould be omitted as far as possible. In amounts up to about 0.4%,however, the carbon has little effect except to increasethe ultimatestrength to a slight extent.

For the purpose of imparting a high standard of resistance to thealloys, especially against attack by certain organic acids, such aslactic, the addition of small amounts of nickel and cobalt has beenfound satisfactory. These metals efiect the result desired when presentin quantities ranging from about 0.5 to about 5%. recommend the additionof aluminum in a quantity of from about 0.2 to about 5% since this metalfurnishes the alloys with an increased resistance at high temperaturesas well as resistance to hot furnace gases. The mechanical properties ofthe alloys as regards workability and formability and resistance toabrasion are also improved by the presence of nickel, cobalt andaluminum.

The balance of the alloy is iron, the iron of course containing thesmall amounts of the usual impurities. Consequently, wherever occurringin the specification and claim, the term iron" is to be so construed.

My invention is further illustrated in the following examples to which,however, the invention is not restricted:

It has been previously stated that'my alloy has mechanical propertiesclosely approaching those of German silver. This fact is clearlydeveloped in the following table which compares certain mechanicalproperties of the alloy of Example 2 with a German silver containing16.9% of nickel, 69.75% of copper, the balance being zinc:

Yield Ultimate Elongapoint strength tiou Kg. per Kg. per meter per meterper sq. meter sq. meter Percent German silver 30. 2 47. 0 30, 0 Alloy ofExample 2 30. 0 58.0 25, 0

It is clear from this comparison that my alloys are similar to Germansilver as to yield point, excel German silver as to ultimate strengthand are capable of only a slightly lower elongation.

My alloy alsopossesses many other valuable characteristics which make itadmirably suitable for use as a substitute for German silver. Thus it ischeaper than German silver. It is capable of being mechanically workedand shaped in either hot Similarly I- or cold condition and in additionmay be worked with chipping tools. Because 01 its low yield point at amoderate ultimate strength, it possesses an especially high flowabilityand hence'may be readily stamped to produce the finest of engravings. Ithas an appearance very closely resembling silver and like silver iscapable ottaking a high glossy polish. It is corrosion-resistant andunlike the corrosion-resisting steels 'at present suggested assubstitutes for German silver can be galvanically coated to producedurable platings of any desired thickness. In short, my alloys possessall the properties necessary to recommend it as a substitute for Germansilver. Thus, my alloy may be used for the manufacture of utensils andthe like which up to now have been manufactured from silver or Germansilver. In

addition it may be used to replace silveror German silver in theformation of armatures,

Percent Manganese 7 -50 Chromium 6 -25 Copper 0.5-10 Carbon Up to 0.4Iron Balance the manganese content being in excess of the chromiumcontent.

ALFRED KROPF.

